Releasable polyester high gloss metal transfer film

ABSTRACT

A carrier film of thermoplastic polyester has releasable metal adhesive properties suitable for a metal transfer in which the polyester film is metalized and the metal layer is subsequently transferred to a permanent adhesive-coated substrate. The metal layer is in direct contact with the polyester carrier film and no intermediate release layer is present. Desired metal adhesion is provided by dispersing an suitable surfactant, and optionally, a hydrocarbon wax, uniformly into the polyester film. Surfactant on the outer surface of the carrier film modifies metal adhesion to the polyester such that the metal can be removed in a metal transfer operation.

FIELD OF THE INVENTION

This invention relates to polyethylene terephthalate (PET) films withrelease properties suitable for transferring metal to substrates, suchas paperboard. More specifically it relates to a metalized PET film ableto receive, carry, and transfer onto a substrate a metal layer directlyin contact with the PET layer of the film.

BACKGROUND OF THE INVENTION

Polymeric films such as PET film are commonly used to transfer metal topaperboard and other substrates for use in packaging, greeting cards,and similar product applications where it is desirable to give theproduct a metallic appearance. The technique of transferring metal fromfilm to another substrate is used where it is not practical to metalizesuch substrates directly.

One typical metal transfer technique uses a metalized conventionalpolymeric film and bonds the complete metalized film structure to thesubstrate. Typical methods for depositing metal onto the polymeric filminclude vapor and sputter metallization processes. Such depositiontechniques typically create strong bonds between the metal and the film.Because metal does not readily separate from the polymeric layer of thefilm, in the transfer procedure the paperboard substrate becomespermanently bonded to the metalized polymeric film. This can createexcessive non-recoverable scrap since the resulting laminate, forexample generated by post-consumer packaging disposal, can not be easilyrecycled.

Another technique that is well known and practiced in industry is tocreate a carrier film that can be used to transfer a metal layer topaperboard and other substrate materials. The carrier film is created bycoating a layer of release material on the base polymeric film in asecondary, separate process from producing the base polymeric film.Subsequently, and in an entirely separate third process, a metal layeris deposited onto the release layer for example by via vapor or sputtermetallization. The individual steps may be carried out at differentlocations by different converters. A disadvantage is that an extraprocessing step is required, in particular the step of applying arelease layer. A need exists for biaxially oriented polyester films thatcan transfer metal from a layer deposited onto the carrier film surfaceto another substrate without the need for costly coatings between themetal layer and the carrier film surface.

The primary function of the release layer is to provide appropriateadhesion between the polymeric film surface and the metal layer. Theadhesion of the metal to the film surface should be strong enough toendure handling in manufacture, packaging, shipping, etc. prior to metaltransfer. However, adhesion should be sufficiently weak that the metallayer cleanly separates from the carrier film surface when contactedwith the substrate.

There is a need for a method of metal transfer from a polymeric film toa substrate in which a metal layer can be applied directly onto thepolymeric film and in which the metal layer readily releases andseparates from the film. It is desirable to have a carrier film thatdoes not have an added release layer on the surface of the polymericfilm. It is further desired to have a carrier film for metal transfer inwhich the base layer is a single polymeric composition that can berecycled after the metal has been transferred. Still further it isdesired to have a polyester-based carrier film and transfer film that isfree of a non-polyester release layer.

Basically, metal is transferred by contacting an adhesive-coatedsubstrate with the metal layer side of the polymeric carrier filmcomposite and then peeling the polymer away to leave the metal on thesubstrate. The ability to make the transferred metal on the substratehighly glossy is very desirable. However, generating a high glossappearance after removing the polymeric film is made problematic byconventional film “anti-blocking” technology. Polymeric film tends tostick to itself and other surfaces, sometimes referred to as “blocking,”during various film handling steps of the metal transfer operations.Typically, blocking is reduced by uniformly dispersing fine inorganicparticles in the polymer of the carrier film. The particles give thefilm a rough surface texture that renders the film less susceptible toblocking. Because the metal layer profile conforms to the carrier filmsurface, after removal the polymer the transferred metal exhibits arough surface texture. Unfortunately, surface roughness reduces glosssuch that the transferred metal has a low gloss or even matte finishedappearance. A very smooth transferred metal surface, for example asmight be formed without particles embedded in the polymer, should havehigh gloss appearance but is impractical to achieve because frictionbetween adjacent polymer film layers makes film handling unmanageable.Thus there is an important need to have a polymeric film free of aseparate release layer that can transfer metal to a substrate withsuperior gloss.

SUMMARY OF THE INVENTION

The present invention provides a single or multi-layered thermoplasticpolyester carrier film for metal transfer that is free of anon-polyester release layer. The composition of the thermoplasticpolyester carrier film is preferably polyethylene terephthalate (“PET”).At least one surface of the novel carrier film is intended forreceiving, carrying and releasing a metal layer in the process oftransferring the metal layer to a substrate, such as paperboard. Themetal receiving surface of the polyester carrier film has suitable metaladhesion and release properties that result from the incorporation ofone or more release agents into the polyester carrier film metal-bearinglayer.

In one aspect, the release agent is a surfactant. The surfactant can bean anionic surfactant, a nonionic surfactant or a combination of anionicand nonionic surfactants. The surfactant is dispersed within the carrierfilm metal-bearing layer. In another aspect the release agent in thenovel polyester-based carrier film is a hydrocarbon composition wax.

Accordingly, the present invention provides a polyester carrier film foruse in metal transfer, the film having a total thickness of about 4-75μm, and consisting essentially of polyester and a release agent ofcomposition and amount effective to provide at least one outer surfaceof the film with metal adhesion of less than 100 g/in. The totalthickness of the polyester film of this invention is preferably about5-75 μm, more preferably about 8-50 μm, and most preferably about 10-25μm.

The invention also provides a method of transferring metal to asubstrate comprising the steps of: (A) providing a polyester carrierfilm having a total thickness of 4-75 μm consisting essentially ofpolyester and a release agent, and (B) depositing a metal layer ofthickness equivalent to an optical density in the range of up to about 4in direct contact with an outer surface of the polyester carrier film,in which the release agent is of composition and amount effective toprovide metal adhesion between the outer surface and the metal layer ofabout 1-100 g/in. Preferably the optical density of the metal layer isabout 0.01-4, and more preferably about 0.4-3.3. Surface resistivity ofthe exposed side of the base layer is not critical, however, ittypically is less than 1×10¹⁷ ohm/square. The carrier film can be acomposite of multiple polyester sub-layers.

In another aspect, this invention also provides a polymeric carrier filmwithout a release layer and having a metal side surface of the carrierfilm polymer suitably smooth to enable transfer of a metal layer onto asubstrate with resulting high metal surface gloss. Desired smoothness ofthe metal side surface of the carrier film polymer is obtained bycontrolling the size and concentration of anti-block agent particlesthroughout the carrier film polymer including the region of the carrierfilm distant from, as well as the region near, the side on which themetal to be transferred is placed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section view of an embodiment of the novelmetal transfer film in proximity to an adhesive coated substrate priorto transferring a metal layer.

FIG. 2A is a surface topography map of the skin layer of the filmproduced with small size dispersed solid particles as further explainedin Example 14.

FIG. 2B is a surface topography map of the skin layer of the filmproduced with large size dispersed solid particles as further explainedin Example 13.

DETAILED DESCRIPTION OF THE INVENTION

In certain aspects this invention relates to biaxially orientedcoextruded multilayer polyester films that can be readily fabricated,have ease of handling, and metal release properties on at least oneouter layer surface, for use in metal transfer processes. To fabricatethis highly specialized film with special surface properties anystandard method to fabricate co-extruded biaxially oriented multilayerfilms may be employed. As used herein, the term “polyester carrier film”refers to a film of polyester and release agent according to thisinvention prior to deposition of a layer of metal thereon. The term“transfer film” refers to a composite of the polyester carrier film witha metal layer of metal deposited on an outer surface of the polyestercarrier film. The primary intended use of the novel polyester carrierfilm is to receive, carry and transfer some or all of the metal from themetal layer onto a surface of a substrate.

The novel polyester carrier film has two sides and has a base layer B ofpolyester. The polyester carrier film can be monolithic consisting onlyof layer B, or a composite of multiple layers of polyester. A preferredembodiment of the invention includes at least a two layer coextrudedpolyester carrier film, that includes at least one outer layer Aadjacent one side of base layer B with an optional opposite outer layerC. Other embodiments may include one or more inner layers I₁, I₂, I₃ . .. I_(n), positioned between the outermost and B layers, such as anA/I₁/I₂/B/C structure, for example. The outermost layers, whether A, B,or C, are sometimes referred to as skin layers. Any layer may containreclaimed polyester resin.

In the present invention either or both outer surfaces of the skinlayers have metal adhesion of less than 100 g/in, preferably less than50 g/in, and more preferably less than 20 g/in, measured as described inTest Methods section below. The metal adhesion property is achieved byblending into the polyester of the film surfactants that are eitherionic, nonionic or a combination thereof. For cost effectiveness it ispreferable that the surfactant component is present only in theoutermost layer or layers, which are normally thinner than the totalthickness of inner layers, i.e., non-skin layers.

Some examples of nonionic surfactants may be cetostearyl alcohol,stearyl alcohol, oleyl alcohol, cetyl alcohol, pentaethylene glycolmonododecyl ether, polyoxypropylene glycol alkyl ethers, octaethyleneglycol monododecyl ether, lauryl glucoside, polyoxyethylene glycoloctylphenol ethers, octyl glucoside, and decyl glucoside.

Some examples of anionic surfactant may be perfluorooctanesulfonate,perfluorobutanesulfonate, sodium dodecylbenzenesulfonate, sodiumsulphate, alkyl benzene sulfonates, dioctyl sodium sulfosuccinate, alkylether phosphate, alkyl aryl ether phosphate, sodium stearate;perfluorononanoate, perfluorooctanoate, sodium lauroyl sarcosinate,sodium myreth sulfate, sodium lauryl sulfate, sodium laureth sulfate,and ammonium lauryl sulfate, and more generally alphatic and aromaticsulphonates.

There are a number of companies that produce master batches ofsurfactant compounds in PET for example, T7910 from Toray Industries,Inc. containing sodium dodecylbenzenesulfonate, Tas1125 from Sukanocontaining an aliphatic sulphonate, or Elecut® S618-A1 from Takemoto Oiland Fat containing a proprietary mixture of nonionic and anionicsurfactants.

As presently understood, the parameter that mainly affects the desireddegree of metal adhesion between the metal layer and an outermostpolyester layer is the surface density, i.e., mass per unit area, ofsurfactant on the outermost surface of the polyester skin layer when themetal layer is applied. Surfactant that is initially uniformly dispersedwithin the polyester resin that forms the skin layer will bloom to thesurface during the carrier film manufacturing process. The amount ofsurfactant incorporated in the polyester resin should take the bloomingeffect into account. That is, as thickness of the of the skin layerdecreases, less surfactant-bearing polyester resin is used, andtherefore, less surfactant at any given surfactant concentration in thepolyester is available to migrate to the surface. Accordingly, theconcentration of surfactant in the polyester resin to achieve apreselected level of metal adhesion should be increased as the thicknessof the corresponding polyester layer decreases. The concentration ofsurfactant by weight in any outer layer should be at least about 0.01 wt%, preferably at least about 0.05 wt %, and more preferably at leastabout 0.10 wt %. The concentration of surfactant by weight in any outerlayer is preferably less than 10 wt %, more preferably less than 5 wt %,and most preferably less than 3 wt %.

An advantageous feature of this invention is that metal adhesion can becontrolled to a preselected value within a narrow range by adjusting theconcentration of release agent in the polyester carrier film. Preferablythe metal adhesion can be controlled to within a range of ±10 g/in of atarget metal adhesion value. Pursuant to the guidelines just described,the actual amount of surfactant will be adjusted depending upon thethickness of the skin layer to provide a suitable metal adhesion valueand should be determined by one of ordinary skill in the art withoutundue experimentation.

Juxtaposition of the elements discussed above can be understood withreference to FIG. 1. The figure shows a cross section of an embodimentof a metal transfer film 10 in proximity to a substrate 15 coated with alayer of adhesive 11. The novel metal transfer film has a multilayercomposite polyester carrier film 1 of three substrata 2, 4 and 6, in theillustrated embodiment. Base layer 2 is a primary component layer of themultilayer carrier film 1. Adjacent and directly in contact with thebase layer are layers 4 and 6. Being outermost layers of the compositepolyester carrier film, layers 4 and 6 are designated as skin layers.

The figure shows that a metal layer 8 is deposited in direct contactwith the side of skin layer 6 opposite the base layer 2. In traditionalmetal transfer films, there is an extra release layer positioned betweenthe metal layer 8 and the outermost layer 6 the function of which hasbeen described above. The novel metal transfer film does not have aseparate and distinct release layer.

In use, an adhesive layer 11 coated onto a receiving substrate 15, isbrought in contact with the metal layer 8 of the metal transfer film 10.The metal layer is then bonded to the substrate by the adhesive layerand thereafter the base layer 1 is stripped away from the metal layer.This process leaves the metal layer attached to the receiving substrateby the adhesive layer 11. An advantage of the novel metal transfer filmis that all of the layers of the carrier film consist essentially ofpolyester. By “consists essentially of” is meant that the polymercontent of the film is at least about 99 wt % and preferably exclusivelypolyester. The film can include, usually in small proportion to thepolymer, and in addition to the operative surfactants, othernon-polymeric ingredients such as stabilizers and additives that do notmaterially affect the novel aspects of the invention. Only the polymericfilm remains after stripping the metal layer. Because the polymericcomponent of every layer of the carrier film is the same polymer,preferably PET, the residual carrier film can be recovered and recycledas a raw material for use in the same or a different end useapplication. Additional aspects, features and advantages of theinvention will be explained, below.

In a primary aspect, the present invention calls for providing a metaltransfer film consisting of a carrier film of predominantly polyesterand a metal layer directly in contact with the carrier film. A releaselayer as used in traditional metal film transfer operations is notpresent between the carrier film and the metal layer. The normally veryhigh metal adhesion of the polymeric carrier film is adjusted to apreselected lower adhesive strength by incorporating a suitable releaseagent into the carrier film polymer. In accord with the principlesdisclosed herein, it is possible to incorporate into a polyester layeran amount of release agent effective to provide a desired degree ofmetal adhesion called for by a converter in a metal transfer filmprocess. The preferred release agent is a surfactant or combination ofsurfactants. Preference is given to use of a mixture of anionic andnonionic surfactants. Optionally, hydrocarbon wax, such as paraffin wax,can be added to any or all layers of the film. Generally, the greateramount of release agent incorporated into the metal-contacting layer ofthe carrier film at a given layer thickness, the lower the metaladhesion and the more easily the metal strips from the transfer film.

The polymeric carrier film can be monolayer or it can be a composite ofmultiple layers of polyester. In a multilayer structure the carrier filmlayers are fused adjacent to each other, preferably by a thermal fusionprocess such as coextrusion such that layers will not delaminate undermetal transfer film processing conditions. A so-called A/B multilayerstructure with a base layer (layer “B”) and a skin layer (layer “A”) ispreferred. The skin layer is the layer in contact with the metal layer.An A/B/C structure is an alternately preferred structure for the novelpolyester-based carrier film in which the “C” layer is a skin layer onthe base layer surface opposite the A layer. Preferably the base layeris the predominant layer in thickness and bulk of the wholepolyester-based carrier film. In a multilayer composite structure, thesurfactant release agent particles should be present at least in themetal-contacting layer, but may also be present in other layers of thecarrier film.

The controlled metal release property of the polyester carrier film isobtained by incorporating surfactant into the carrier film, andpreferably in only one or more of the outer layers. Preferably thesurfactant is an anionic surfactant, a nonionic surfactant or acombination thereof. Metal adhesion of PET without an incorporatedsurfactant release agent is typically much greater than 150 g/in.Incorporation of surfactant according to this invention can providemetal adhesion of less than 100 g/in, preferably about less than 50g/in, and more preferably less than 20 g/in.

In some end use applications it is desirable to transfer effectively allof the deposited metal whereas in other cases it is desirable totransfer only specific portions of the metal. According to thisinvention, all or any selected parts of the metal deposited onto thesurface of the base layer may be readily transferred to the substrateutilizing well known techniques.

Typical schemes for a metal transfer process call for providing carrierfilms from film “converters”, i.e., suppliers and processors of film whoprovide, treat and/or modify the polyester film in secondary operationsthat are entirely separate from and subsequent to the manufacture of thepolyester film. Such polyester carrier films include a non-polyestercomposition release layer coating applied to an outer surface of amonolithic polyester film. Those films are in turn metalized on therelease layer via a process such as vapor deposition or sputtering. Themetal transfer film of polymeric base layer/release layer/metal layerstructure is used to apply metal to substrate products such aspaperboard that are not directly metalizable by conventional means. Thepaperboard converters specify, and the film converters supply, desireddegrees of metal adhesion based on the nature of the product and themetal. An advantage of this invention is the ability to control the bondstrength of the metal to the PET base layer to a preselected valuewithin the range of metal adhesion normally desired by paperboardconverters. The metal transfer film of this invention does not have aspecial, non-polyester-based release layer between the base layer andthe metal. Thus the polyester base film metalizing converter can applythe metal in direct contact with the polyester base layer of the carrierfilm. An intermediate release layer typically applied as a coating onthe base film is not required. This feature provides many productivityenhancing and cost saving benefits. It is especially valuable that theconcentration of surfactant and optional wax release agent incorporatedinto the polymeric base layer can modify the metal adhesion of thecarrier film to match the different specifications for diverse metaltranfer end use applications of metal transfer converters. Thisinvention further can provide metal adhesion with precision of narrowtolerance limits of the metal transfer converters' target.

Processing of film at commercial scale normally demands moving, rollingand unrolling, among other procedures, of wide webs of the film at highspeed. In such unit operations the webs have opportunities to come incontact with each other and with the processing equipment. Friction cancause the contacting webs to stick together or to jam the equipmentconsequently generating substantial waste product and lost productivity.Stagnant film, for example, when stored on a heavy roll for extendedtime, can also stick to itself. This condition is known as “blocking” inthe industry. Giving a rough texture to the potentially contactingsurfaces of the film is a way to control friction and thereby partitionthe webs from themselves and machinery. A preferred technique forroughening the surface involves embedding fine, solid, anti-blockingagent particles into a layer of the film. The particles at and near thesides of the film form irregularities that make the surface rough.

Texture of the carrier film surface in contact with the metal can shapethe metal layer surface transferred onto the substrate. Degree ofsurface can affect visual appearance of the finished metal-coatedsubstrate product. Usually, rough surface texture gives a dull, mattefinish, and conversely, a smooth surface texture gives a shiny, glossfinish. As used herein, a smooth surface is defined as having surfaceroughness Ra of about 100-150 nm. A more smooth surface has Ra of about50-100 nm, and a very smooth surface has Ra of about 5-50 nm. A roughsurface typically suitable to produce a matte appearance of thetransferred metal, has an Ra of about 200-500 nm. The symbol “Ra” meansa surface roughness measured with a “surfcorder” analytical device, forexample, a SurfCorder SE 500 Surface Roughness Measuring Instrument(Kazaka Laboratory Ltd. Tokyo, Japan).

A problem addressed by this invention is the creation of a very highlyglossy surface effect, referred to herein as “high metal surface gloss”of a substrate onto which a metal layer is applied by peeling away thecarrier film from a metal transfer film. Thus a high metal surface glosshas a remarkably shiny, bright metallic appearance to the visualobserver. The invention provides for producing a high metal surfacegloss appearance using a metal transfer film without a release layerbetween the carrier film and the metal layer being transferred.

Total reflection of light impinging on an object is characterized by thetwo components of specular reflection and diffuse reflection. Gloss isan optical property of a surface related specular reflection which ismirror-like reflection of light in a specular direction at an angleequal to the incident angle. Diffuse reflection is light reflected atall angles. Factors that affect gloss are the refractive index of theilluminated object, the incident angle of light impinging on the object,and the surface topography (i.e., roughness) of the object. Respectingtopography, the fraction of reflection that is specular increases withsmoothness. Increased roughness caused by irregularity of the surfacetopography decreases the fraction of specular reflection. Roughness cancontribute to reduced specular reflection in two ways. Firstly,curvature of the irregular surface contour scatters impinging light byreflecting at different angles. Secondly, specularly reflected lightfrom surface locations at different elevations creates can have acanceling effect due to mutual specular beam interference. The firstaspect can make the illuminated object appear dull. The second aspecthas a light attenuating effect. The presence of fine, solid particlesdispersed in a layer of polymeric film cause localized variations in thethickness of the film and thereby affects surface roughness. Thusincorporation of selected size distributions of particles at selectedconcentrations is a primary technique for controlling surface roughnessof a film. The term “high metal surface gloss” means that the finished,metal-coated surface of the substrate exhibits specular reflection glossof at least about 830 gloss units (“GU”) by glossmeter measurement at60° angle. The ability to achieve high metal surface gloss product isenhanced by utilizing a metal transfer film (i.e., polymeric carrierfilm with metal coating) that exhibits surface smoothness of at leastabout 860 gloss units measured at 60° angle and at least about 1300gloss units measured at 20° angle. Moreover, the smoothness of themetal-contacting side of the polymeric carrier film prior to metaldeposition should correspond to at least about 180 gloss units at 60°angle.

It also has been found that a high metal surface gloss can be obtainedby transfer of metal from the novel polymeric carrier film of which thepolymer-to-metal surface has a Surfcorder surface roughness, Ra,preferably at most about 50 nm, and more preferably at most about 30 nm,still more preferably at most about 25 nm, and most preferably at mostabout 15 nm. An Ra value as low as about 0 nm is theoretically suitableto provide the desired gloss but is impracticable to achieve. PreferablyRa can be at low as about 12 nm and more preferably about 15 nm.Similarly acceptable gloss performance is obtained when the polymericcarrier film surface has a stylus surface roughness value, Sm, in therange of about 0-30, preferably about 10-30 and more preferably about10-15. Stylus surface roughness is determined using a stylus typecontact profilometer, for example a Surfcorder ET-30 HK surfacetopography instrument (Kosaka Laboratory Ltd, Tokyo Japan). Mostpreferably, the carrier film surface should have both Ra of about 12nm-30 nm and an Sra value of about 10-30.

Carrier film surface roughness that provides high metal surface gloss isachieved by controlling the size and concentration of anti-block agentparticles dispersed in the polymeric film. Theoretical Ra and Sra valuesof about 0 should be achieved from a polymeric film having no anti-blockagent particles present. This condition is not practicable becausesubstantially complete absence of anti-block agent particles renderssurface friction of the carrier film too high for handling the film incommercial scale industrial fabrication and processing equipment. Thusfor practical purposes, some anti-block agent particles should beuniformly dispersed in the polymer of the carrier film. Of course, ifthe particle size and/or concentration of any particles for anti-blockor other purposes, such as pigmentation, is too great, the surface ofthe transferred metal will be too rough and finished appearance will beless glossy than high metal surface gloss.

For adequate surface roughness to enable manageable handling of the filmand yet to obtain surface smoothness consistent with high metal surfacegloss the nominal particle size of anti-block particles suitable for usein this invention is preferably about 0.1 μm to about 2.4 μm, morepreferably about 0.1 μm to about 2.0 μm and most preferably about 0.1 μmto about 1.0 μm, and the concentration of the anti-block particles ispreferably about 0.01 wt % to about 1.0 wt %, and more preferably about0.01 wt % to about 0.05 wt %.

As mentioned above, it is contemplated to use multi-layer composites,e.g., A/B/C layered structure, for the polymeric carrier film. Applyinga layer of metal, M, to an exposed surface of the carrier film thusprovides a metal transfer film with an M/A/B or M/A/B/C structure inwhich A and C are polymeric skin layers and B is a polymeric core layer.In such situations, it is advantageous to disperse anti-block agentparticles of partitioning effective size and concentration only inoutermost layers B or C as the case might be. That is, metal-contactinglayer A would have no particles and the M/A interfacial surface keptvery smooth for highly glossy metal transfer performance.

It can be problematic for obtaining high metal surface gloss after metaltransfer if excessively large or high concentrations of particles arepresent in layers adjacent to, and even distant from, metal contactingskin layer A. Particles are deliberately incorporated into outer layersB or C for anti-blocking purposes. Also particles can be allowed intolayer B of an A/B/C structure when all or part of the polymer stream oflayer B is scrap or recycled polymer that is contaminated with solidparticulate matter. Excessively large particle sizes and concentrationstend to protrude into skin layer A and can adversely affect roughness ofthe metal contacting surface. Caution should be exercised to avoid toolarge or concentrated anti-block agent particles in layers B and C thatwill cause surface of layer A roughness parameters Ra and Sra to exceedthe preferred limits specified above.

This invention further advantageously provides the ability to utilize anA/B/A polymeric carrier film. This structure can be producedeconomically by unit operations equipped with only two extruders, i.e.,one for each of layers A and B compositions. This set up can simply anddirectly make an A/B carrier film. Alternatively, flow from a singleskin composition extruder can be split to feed A composition onto bothsides of B to yield the A/B/A structure. The surface of themetal-contacting layer A should be smooth enough to enable transferredmetal with high metal surface gloss. The surface of thenon-metal-contacting layer A should be rough enough to providemanageable film handling. It has been found that an A/B/A compositecarrier film suitably satisfying both gloss and film handling criterialcan be made when Ra and Sra parameters of layer A are within the rangesspecified above.

Preferably according to this invention anti-block agent particles shouldbe smaller than about 1 μm. However, when the core and/or skin layer onthe metal-contacting side of the carrier film are suitably thick to maskthe effect of large concentrations or large size of particles dispersedin a layer distant from the metal-containing side, larger particles canbe used. For effective masking, the total thickness of layers B, and C,preferably should be at least as great as the largest particles in suchdistant layers. For example, in a metal/skin layer/core layer/skin layermetal transfer film M/A/B/C, larger size particles, i.e. particlesnominally bigger than 1 μm, and larger concentrations of particles canbe tolerated only in layer C, provided that layers A and B have acombined thickness large enough to smooth perturbations of the M/Ainterfacial surface that would otherwise result from the particles inlayer C.

According to this invention, the overall thickness of the carrier filmis preferably about 5 μM to about 75 μm, more preferably about 8 μM toabout 50 μM and most preferably about 10 μm to about 25 μM. Thickness ofthe metal-contacting skin layer A, and, when applicable, skin layer C,should be preferably about 0.5 μm to about 5 μm. Thickness of the corelayer is the difference between the total carrier film thickness and thetotal thicknesses of the skin layers present. Typically, the core layeris the thickest layer of the carrier film. Thickness of the metal layeris typically less than about 4 optical density units that correspondsapproximately to 500 angstroms. The metal layer thus adds negligibly tothe overall thickness of the metal transfer film. Many types ofanti-blocking particles may be used such as silica, calcium carbonate,talc, alumina, or polymeric particles, such as, cross-linkedpolystyrene, acrylic, polyamide, or combinations thereof.

The smoothness characteristics for a high metal surface gloss qualityspecified above relate to the surface of the carrier film facing themetal being transferred. The surface of the side of the carrier filmopposite the metal-contacting side can be less smooth. Thenon-metal-contacting side surface can have an Ra of about 5-250 nm,preferably about 5-150 nm, and more preferably about 5-50 nm. Theoptional wax release agent can be included in one or more film layers tomodify the release characteristics of the film provided by thesurfactant primary release agent. The wax need not be added to the outerrelease layer in order to be effective since the wax will migrate fromwithin the film through the outer layers to the surface of the filmduring stretching and heat setting processes of film making. The wax canbe added as a separate additive to the polyester resin when forming acarrier film layer. A preferred method of adding wax release agent to aspecific layer includes recovering a waste or discarded polyester filmthat originally had a paraffin wax coating. The wax-coated film isrecycled by shredding the film to fine particle size, agglomerating theshredded film by use of a bladed centrifuge process, and thenre-extruding the wax containing resin into pellets. The resultingrecycled resin pellets can be blended with other raw material resin andadditional wax, as appropriate to form one or more layers of thepolyester carrier film. Typically, the wax is about 0.1-1 wt. % ofrecycled polyester film. Any wax-containing layer of the novel carrierfilm can contain up to 100 wt. % of recycled polyester film.

Without wishing to be bound by any particular theory, it is contemplatedthat the primary mechanism for modifying adhesion of the metal layer topolyester of the carrier film is the creation during metalization of ametal oxide layer between the polyester and the pure metal layers. Thesurfactant at the surface of the polyester carrier film supplies oxygenat this surface. Surfactants containing nitrate ion, sulfate ion, alkylsulfate ion, sulfonate ion, or alkyl sulfonate ion are very suitable inthis regard. Metal deposition methods for metalizing films typicallyinclude first evacuating oxygen from vapor, usually air, in the chamberin which metalization is to be carried out. This permits highly puremetal to deposit on and bond with the carrier film polymer. According tothis invention, oxygen brought to the polymer surface by the surfactantrapidly (i.e., normally within a few minutes) reacts with the metal tocreate a layer of metal oxide between the polyester carrier film and thebulk of the deposited metal layer more distant from the surface. Theresulting metal oxide layer is less adhesive to the polyester and thusfacilitates release of the metal layer during the later metal transferoperation.

It is thus understood that this invention is particularly well suited tometal transfer operations involving any metals that readily oxidize.Metals commonly used are aluminum, copper, silver, titanium, and amixture of these.

One preferred embodiment of the novel carrier film is a two layer PETfilm structure in which one layer is a skin layer with a thickness ofpreferably about 0.1-10 microns, more preferably about 0.2-6 microns,and most preferably about 0.3-2 microns. The second carrier film layerconstitutes most of the the structure thickness that is preferably about5-75 microns, more preferably about 8-50 microns, and most preferably10-25 microns. The second carrier film layer optionally contains waxadded from ground, recycled, paraffin wax-coated film. The skin layerhas a surface roughness, Ra, of preferably about 5-50 nm, morepreferably about 5-30 nm, and most preferably about 5-15 nm.

Another preferred embodiment is a three layer PET film structure inwhich the non-skin carrier film layer is substantially free of addedparticles. One or both skin layers have release properties byincorporation of surfactants. The skin layers preferably have athickness of about 0.1-5 microns, more preferably about 0.2-3.6 microns,and most preferably about 0.3-2 microns. The non-skin carrier film layercan contain wax release agent from addition of recycled paraffin waxcoated film. The carrier film has a thickness of about 5-75 microns,more preferably about 8-50 microns, and most preferably about 10-25microns.

The polyester for use in this invention can be prepared by any knownmethod such as by the polycondensation of terephthalic acid or anester-forming derivative thereof with an alkylene dihydroxyl compound.For example, these polymers can be copolymers of repeating units derivedfrom aromatic dicarboxylic acid aliphatic glycol. Examples of suitablearomatic dicarboxylic acid are terephthalic acid, napthalenedicarboxylacid, isophthalic acid and the like. Examples of aliphatic glycol areethylene glycol, butanediol, neopentyl glycol, trimethylene glycol,cyclohexane dimethanol and the like. Examples of polyesters for use inthe invention include copolymers coprising alkylene terephthalate oralkylene napthalenate as the main recurring units in the polymer chain.A preferred polyester is polyethylene terephthalate.

EXAMPLES

This invention is now illustrated by examples of certain representativeembodiments thereof, wherein all parts, proportions and percentages areby weight unless otherwise indicated.

Test Methods

Thickness: Overall film thicknesses were measured by micrometer using astack of 10 sheets and dividing the measurement by 10. Measurements wererepeated every 9 inches in the transverse direction of the web. Thethickness of each coextruded layer of the multilayer film was calculatedby the ratio of the corresponding extrusion flow rate to the totalextrusion flow rate of all layers.

Metal Adhesion: Metal adhesion was measured by a 180 degree ethyleneacrylic acid polymer peel test consisting of heat sealing an adhesivelayer of Dow Primacor® 3300 EAA polymer to the metalized side of thefilm using a Sentinel Model 12-ASL Sealer at 220° F. and 38 psi for 20seconds. An Instron® 4200-004 tensile test machine was used to measurethe peel force to peel away the metal with the adhesive layer at 180degrees from the metalized surface of the film.

Surface Roughness: Surface roughness (“Ra”) was measured by a SurfcorderModel SE-500 surface roughness measurement instrument. The measurementswere repeated 3 times and the average value of Ra was recorded. Surfacemapping and Sra roughness analysis was performed according to the HIPOSS(High Precision Optical Surface Sensor) method using a Stylus typesurface topography analysis instrument Surfcorder ET-30 HK, equippedwith an SSC Surface Picture Analyzer type SPA-1 and an SSC X-Y chartrecorder type RA-XY 4A (all manufactured by Kosaka Laboratory Ltd.)

Surface Resistivity: Surface resistivity was measured with a concentricring probe from TREK, Inc, Model No. 152 concentric ring proberesistivity meter according to ASTM Standard D 257-99. The testingconditions were 25° C. at 50% of relative humidity.

Surface Energy: Surface energy was determined by using the knownnumerical relationship between surface tension in dynes/cm of a polymersurface and the contact angle of a pure water drop deposited onto thesurface (Zisman correlation). The contact angle was measured using aContact Angle Meter (from Tantec, Schaumberg, Ill.) as described in U.S.Pat. No. 5,268,733.

Surface gloss: Surface gloss was measured at 60° angle (and at 20° anglewhere noted) according to ASTM D 523 using a Micro TRI-Gloss Meter fromBYK-Gardner. Three individual measurements along the machine directionof film formation (MD) and three along the transverse direction (TD)were conducted. The overall average of all six measurements is reported.The results are expressed in Gloss Units. The measurement results of agloss meter are related to the amount of reflected light from a blackglass standard of defined refractive index that defines a standard glossmeasurement value of 100 gloss units. Material to be measured with ahigher refractive index than the standard, such as polymeric film, canhave a measurement value above 100 gloss units (GU). Typically, metallicsurfaces measure values above about 700 GU at 60° angle and above about1500 at 20° angle.

Procedure: Three layer PET carrier films having A/B/C layer structureand two layer films having A/B layer structure for the examples wereprepared by the following method. PET and ingredients listed in Table I,below, for each layer were blended, dried and then extruded inconventional melt extrusion equipment. To produce base layer B a serialset of single screw extruders was used. Reclaimed PET film wasoptionally included in this layer. For the composition of layers A andC, PET plus the other ingredients were mixed and fed through acounter-rotating twin screw extruder and dried via in-line vacuum in themelt zones of the extruder. Extrusion temperatures were in the range of270° C. to 300° C. The melt flows from each extruder was filteredseparately and then fed into a melt distributor such that the melt flowfrom the twin screw extruder was split to form layers A and C that wereoverlaid onto opposite sides of the melt flow forming layer B to form anoverall A/B/C structure. To produce a two layer A/B structure, the twinsscrew extruder melt flow was overlaid only on one side of the base layermelt flow. The resulting combined melt flow entered a flat die set atabout 270° C. The melt curtain exiting the die dropped and waselectro-statically pinned onto a rotating casting roll chilled to about20° C. causing the curtain to solidify into a continuously movingamorphous sheet. This sheet entered a set of rotating heated rolls ofdifferent speeds such that the traveling sheet was oriented about 4times in the machine direction. Next, this machine-direction orientedsheet traveled into a multi-zone enclosed heated oven, where the filmwas first preheated to a temperature of about 90° C. In the next zone,at about 165° C., the moving film was oriented about 4 times in thetransverse direction, and then heat set at about 240° C. Then the filmwas relaxed by about 3% in the relaxation zone of the oven. Theresulting two layer A/B and three-layer A/B/C films were wound up intorolls as is standard industry practice.

Comparative Example 1

A two layer PET carrier film was prepared by coextruding adjacent skinlayer A and base layer B. Inert filler particles were dispersed in eachof the molten polymer feeds to the film forming unit. Thickness andcomposition of the layers is shown in Table I. The concentrations andsizes of the particles gave the outer surfaces of the layers differentsurface roughnesses. No metal release agent according to this inventionwere included in the layers. The outer layers had surface resistivity onthe order of magnitude of 1016 ohms/sq. Analytical results for this andother examples are presented in Table II. The surfaces of layers A and Balso had surface energies typical for PET film as indicated by surfacetensions of 40 dynes/cm.

The surface of skin layer A was metalized with a layer of aluminum ofthickness equal to a measured optical density of 2.5 by metal vapordeposition. Metal adhesion was of the aluminum layer on layer A wasmeasured as 135 Win. This is a high adhesion strength and would not besuitable for a metal transfer film.

Example 2

A two layer PET carrier film was prepared as in Comp. Ex. 1 with theexception that a release agent surfactant particles of sodiumdodecylbenzenesulfonate at concentration 0.48% was uniformly dispersedinto skin layer A. Surface resistivity of layer A was much reduced(order of magnitude of 1011 ohms/sq.) and the surface tension increasedto surface tension of greater than 53.5 dynes/cm. The carrier film wascoated with aluminum to an optical density of 2.5. Metal adhesion wasmeasured to be 45.7 g/in. This represents a significant reductionrelative to Comp. Ex. 1 The surface resistivity of layer B loweredslightly (relative to Comp. Ex. 1) but was still at the 1014 level.

Example 3

The procedure of Ex. 2 was repeated except that a blend of release agentsurfactants alkane sulphonate (0.06%) and sodium sulfate (0.003%) wasincorporated in skin layer A. Layer A had a surface resistivity on theorder of 1016. Following aluminum metalization, metal adhesion wasmeasured to be 26.7 g/in. The transfer film would be suitable for ametal transfer film.

Example 4

The procedure of Ex. 2 was repeated except that aliphatic sulphonate wassubstituted as the surfactant release agent at 0.015% in skin layer A.The surface resistivity reduced to a relatively low value of the orderof magnitude of 1012 ohms/sq. After coating the skin layer with a 2.5optical density thickness metal layer of aluminum, the metal adhesionwas measured to be a very acceptable value of 11.2 g/in.

Example 5

The procedure of Ex. 4 was repeated except that the concentration of thesurfactant release agent was doubled to 0.03%. Resistivity of layer Adropped to the 1010 range. After depositing aluminum to an opticaldensity of 2.5, the metal adhesion was found to also drop to 11.2 g/in.that is very good for many metal transfer operations.

Examples 6 and 8

In these examples the procedure of Ex. 2 was repeated with a mixture ofanionic/nonionic surfactants serving as the release agent. In Ex. 6 theconcentration of the surfactant was 1.2% and in Ex. 8 the theconcentration was raised to 2.0%. Again, resistivities of the B layerremained at the 1014 level. The surfactant containing layer A showednearly equal and significant resistivity reduction relative to Ex. 1.After coating with aluminum, metal adhesion of the 1.2% surfactantsample was well in the range of suitable metal transfer film at 7.9g/in. Increasing the concentration to 2.0% surfactant lowered the metaladhesion farther to 6 g/in.

Example 7

The procedure of Ex. 2 was repeated except that the polymer of layer Awas a blend of 50% virgin PET and 50% Auriga PET resin “8428”. TheAuriga PET resin contains surfactant. The surface resistivity of layer Adid not change from that of Comp. Ex. 1 however, metal adhesion of thecarrier film to the aluminum layer did reduce to 33.3 g/in, which iswell into the acceptable range for metal transfer films.

Example 9

The procedure of Ex. 2 was repeated with the exception that 0.48% sodiumdodecylbenzenesulfonate was added to thicker layer B as well as layer A.Due to the presence of surfactant in both layers, resistivities of bothsurfaces dropped to the approximate 1011 level. After metalization to2.5 optical density with aluminum, the metal adhesion of layer A wasdetermined to be 6.3 On. This result suggests an interaction between thelayers in that the effect of the same surfactant at the same level inlayer A was much enhanced by the surfactant in the adjacent layer B.

Example 10

The procedure of Ex. 6 was repeated except that 1.2% mixedanionic/nonionic surfactant was incorporated into thicker layer B aswell as in layer A. Comparing this example to Ex. 6, it appears that theanalytical results were somewhat analagous to those of Ex. 9. Thesurface resistivities of both A and B layers dropped by four orders ofmagnitude relative to Comp. Ex. 1. Additionally, the metal adhesion oflayer A of 4.8 g/in. was significantly lower than in Comp. Ex. 1 andslightly lower than 6 g/in. of Ex. 6. Thus there is agreement with thesuggestion that some interaction between the layers due to presence ofthe same release agent surfactant in both on the metal adhesion value oflayer A.

Example 11

The procedure of Ex. 8 was repeated with the exception that theadditives composition of layer B was changed. Firstly the 0.3 μmpolystyrene particles incorporated into layer B at 0.06% was replaced by0.3% of 2.4 μm silica particles. Additionally, layer B included 0.05%paraffin wax release agent. Analytical results showed that surfaceresistivity of layer A dropped similarly as in Ex. 8 to the 1010 leveland that the metal adhesion reduced to a very low value of 2 g/in. Thelower metal adhesion value further supports the suggestion that wax fromlayer B affects adhesion on the surface of layer A. Example 11 also hasa relatively high surface energy of greater than 53.5 dynes/cm.

Example 12

A three layer PET film carrier film is prepared by coextruding an A/B/Ccomposition and structure. Both skin layers A and C have the samecalcium carbonate/aluminum oxide particle package for modifying thesurface texture and a release agent of mixed anionic/nonionic surfactantat 2.0% concentration. The base layer B includes a silica particlecomponent and 0.013% paraffin wax release agent. The surface of layer Awas metalized with aluminum to a thickness equivalent to 2.5 opticaldensity. The metal adhesion of the carrier film to the metal layer was5.1 g/in.

Example 13

A two layer PET carrier film was prepared by coextruding (1) a 1.2 μmthick skin layer A of PET containing 1 wt % mixture of sodiumdodecylbenzenesulfonate anionic surfactant a nonionic surfactant, 0.33wt % of 0.1 μm size alumina particles and 0.11 wt % of 1.0 μm sizecalcium carbonate particles, and (2) an adjacent 10.8 μm thick, baselayer B of PET containing 0.04 wt %. of 2.4 μm size silica particles.The filler particles were dispersed uniformly in each of the moltenpolymer feeds to the film forming unit. The concentrations and sizes ofthe particles gave the outer surfaces of the layers different surfaceroughnesses. The skin layer side of the carrier film was metalized withaluminum to an optical density of 2.2. Metal adhesion to the skin layerwas determined to be 1.3 g/cm (3.4 g/in.). A layer of adhesive wascoated onto the metal side of the metalized film. A substrate article ofpaperboard was placed into contact with the adhesive layer and thepolymeric carrier film/metal/adhesive/paperboard composite was insertedin the nip between a pair of compression rolls then passed through anoven to cure the adhesive. The polymeric carrier film was peeled fromthe substrate leaving a metal coating exposed on the paperboard surface.Surface roughness and gloss values of the clear carrier film prior tometalization, the metal transfer film of metalized carrier film, andmetal surface of the substrate article after the metal had beentransferred to it from the carrier film are presented in Table III. Skinlayer A surface topography of the A/B carrier layer film is shown inFIG. 2B.

Example 14

A 1.2 μm thick PET skin layer, A, a 9.6 μm thick PET core layer, B, anda 1.2 thick PET skin layer, C, were coextruded to form an A/B/Cmultilayer carrier film structure. Both skin layers A and C contained 2wt % mixture of sodium dodecyl-benzenesulfonate and a nonionicsurfactant, 0.11 wt % of 1.0 μm size calcium carbonate particles and0.33 wt % of 0.10 μm size alumina particles dispersed therein. The corelayer B includes 0.01 wt % of 0.1 μm size alumina particles. The surfaceof layer A was metalized with aluminum to a thickness equivalent to 2.2optical density. The metal adhesion of the aluminum to the carrier filmwas 1.2 g/cm (3.1 g/in). Metal was transferred from the metal transferfilm to paperboard as described in Ex 13. Surface roughness and glossdata are presented in Table III. Skin layer A surface topography of theA/B/C carrier film is shown in FIG. 2A.

Example 15

A 1.2 μm thick PET skin layer, A, a 16.1 μm thick PET core layer, B, anda 1.2 μm thick PET skin layer, C, were coextruded to form an A/B/Cmultilayer carrier film structure. Both skin layers A and C contained 2wt % mixture of sodium dodecyl-benzenesulfonate and a nonionicsurfactant, 0.17 wt % of 1.0 μm size calcium carbonate particles and0.33 wt % of 0.10 μm size alumina particles dispersed therein. The corelayer B includes 0.01 wt % of 0.1 μm size alumina particles. The surfaceof layer A was metalized with aluminum to a thickness equivalent to 2.2optical density. The metal adhesion of the aluminum to the carrier filmwas 1.2 g/cm (3.1 g/in). Surface roughness and gloss data are presentedin Table III.

Example 13 demonstrates a practical implementation of using a releaselayer-free polymeric carrier film to transfer metal to a commerciallyuseful substrate. Gloss of the transferred metal on the paperboardsubstrate is about equivalent to a good quality, state of the art glossfinish. Particles in the core layer were relatively large (2.4 μm). Thisexample shows that such particles in the core layer can affect surfacetopography of the carrier film metal-contacting layer as seen in FIG. 2B(rougher) compared to FIG. 2B (smoother). Surface roughness likelycontributed to slightly muted film and metal gloss values. In Example14, a release layer-free, polymeric carrier film is able to provide aremarkably bright and shiny finish that is well within the gloss unitrange for very desirable, high metal surface gloss. Size of particles inlayers distant from the metal-contacting skin layer is reduced comparedto Ex. 13 contributing to the smoother surface topography seen in FIG.2A.

Example 15 is very similar in structure to Ex. 14 with the mainexception that high concentration (i.e., 0.17 wt % vs 0.11 wt %) of 1.0μm size, calcium carbonate particles were used in the metal-contactingskin layer A. The very moderate increase in particle concentrationcaused the gloss to diminish relative to Ex. 14 while maintaining nearlythe same Ra measured surface roughness. Appearance of carrier and metaltransfer film was acceptable yet slightly less appealing than thepreferred high metal surface gloss evident in Ex. 14. Thus Ex. 15 showsthat the high metal surface gloss is importantly sensitive to a numberof factors that include concentration of embedded particles, size of theparticles in the metal-contacting skin layer and size and concentrationof particles in layers distant from the metal-contacting skin layer.

TABLE I A/B/C Layer Thickness A Layer B Layer B Layer Other C Layer (μm)Polymer A Layer Other Components Polymer Components Composition Comp.  5/28/0 PET 0.4 wt % 0.9 μm CaCO₃ PET 0.06 wt % 0.3 μm none Ex. 1polystyrene Ex. 2   5/28/0 PET 0.4 wt % 0.9 μm CaCO₃ PET 0.06 wt % 0.3μm none 0.48 wt % Sodium dodecyl- polystyrene benzenesulfonate Ex. 3  5/28/0 PET 0.4 wt % 0.9 μm CaCO₃ PET 0.06 wt % 0.3 μm none 0.06 wt %Alkane sulphonate polystyrene 0.003 wt % Sodium sulphate Ex. 4   5/28/0PET 0.4 wt % 0.9 μm CaCO₃ PET 0.06 wt % 0.3 μm none 0.015 wt % AliphaticSulphonate polystyrene Ex. 5   5/28/0 PET 0.4 wt % 0.9 μm CaCO₃ PET 0.06wt % 0.3 μm none 0.03 wt % Aliphatic Sulphonate polystyrene Ex. 6  5/28/0 PET 0.4 wt % 0.9 μm CaCO₃ PET 0.06 wt % 0.3 μm none 1.2 wt %mixture of sodium polystyrene dodecyl-benezesulfonate and a nonionicsurfactant Ex. 7   5/28/0 50 wt % virgin 0.4 wt % 0.9 μm CaCO₃ PET 0.06wt % 0.3 μm none PET polystyrene 50 wt % Auriga 8428 PET Ex. 8   5/28/0PET 0.4 wt % 0.9 μm CaCO₃ PET 0.06 wt % 0.3 μm none 2.0 wt % mixture ofsodium polystyrene dodecyl-benezesulfonate and a nonionic surfactant Ex.9   5/28/0 PET 0.4 wt % 0.9 μm CaCO₃ PET 0.06 wt % 0.3 μm none 0.48 wt %Sodium dodecyl- polystyrene benzenesulfonate 0.48 wt % Sodium dodecyl-benzenesulfonate Ex.10   5/28/0 PET 0.4 wt % 0.9 μm CaCO₃ PET 0.06 wt %0.3 μm none 1.2 wt % mixture of sodium polystyrenedodecyl-benzenesulfonate 1.2 wt % mixture of and a nonionic surfactantsodium dodecyl- benzenesulfonate and a nonionic surfactant Ex. 11  5/28/0 PET 0.4 wt % 0.9 μm CaCO₃ PET 0.3 wt % 2.4 μm silica none 2.0wt % mixture of sodium 0.05 wt % paraffin wax dodecyl-benzenesulfonateand a nonionic surfactant Ex. 12 1.2/22/1.2 PET 0.13 wt % 1.0 μm CaCO₃PET 0.075 wt % of 2.4 μm Same as 0.3 wt % 0.1 μm Al₂O₃, silica Layer A2.0 wt % mixture of sodium 0.013 wt % paraffin waxdodecyl-benzenesulfonate and a nonionic surfactant Ex, 13 1.2/10.8/0 PET0.13 wt % 1.0 μm CaCO₃ PET 0.04 wt % 2.4 μm none 0.3 wt % 0.1 μm Al₂O₃,Al₂O₃ 1.0 wt % mixture of sodium dodecyl-benzenesulfonate and a nonionicsurfactant Ex, 14 1.2/9.6/1.2 PET 0.11 wt % 1.0 μm CaCO₃ PET 0.01 wt %0.1 μm Same as 0.33 wt % 0.1 um Al₂O₃, Al₂O₃ Layer A 2.0 wt % mixture ofsodium dodecyl-benzenesulfonate and a nonionic surfactant Ex. 151.2/16.1/1.2 PET 0.17 wt % 1.0 μm CaCO₃ PET 0.01 wt % 0.1 μm Same as0.33 wt % 0.1 μm Al₂O₃, Al₂O₃ Layer A 2.0 wt % mixture of sodiumdodecyl-benzenesulfonate and a nonionic surfactant

TABLE II A Layer B Layer A Layer B Layer Surface Surface Surface SurfaceA Layer Resistivity Resistivity Tension by Tension by Metal A Layer at25 deg C., at 25 deg C., contact contact Thickness Metal 50% RH 50% RHangle angle (optical Adhesion (ohms/sq) (ohms/sq) (dynes/cm) (dynes/cm)density) (g/in) Comp. Ex. 1 1.8 × 10¹⁶ 3.1 × 10¹⁶ 40 40 2.5 135 Ex. 21.1 × 10¹¹ 1.6 × 10¹⁴ >53.5 40 2.5 45.7 Ex. 3 2.2 × 10¹⁶ 2.5 26.7 Ex. 41.1 × 10¹² 2.5 11.2 Ex. 5 4.3 × 10¹⁰ 2.5 7.9 Ex. 6 1.4 × 10¹⁰ 6.5 ×10¹⁴ >53.5 41 2.5 6 Ex. 7 1.9 × 10¹⁶ 2.5 33.3 Ex. 8 1.2 × 10¹⁰ 5.7 ×10¹⁴ >53.5 41 2.5 5.2 Ex. 9 8.0 × 10¹⁰ 1.6 × 10¹¹ >53.5 >53.5 2.5 6.3Ex. 10 1.6 × 10¹⁰ 1.1 × 10¹⁰ >53.5 >53.5 2.5 4.8 Ex. 11 1.2 × 10¹⁰ >53.52.5 2 Ex. 12 2.5 5.1 Ex. 13 2.2 3.4 Ex. 14 2.2 3.1 Ex. 15 2.2 3.1

TABLE III 20° Gloss 60° Gloss 60° Gloss 60° Gloss Metalized TransferredRa Sra Clear Metalized Carrier Metal (nm) (nm) Film Film Film SurfaceEx. 13 52 32 164 859 1625 795 Ex. 14 26 12 186 878 1775 836 Ex. 15 23176 864 1683

Although specific forms of the invention have been selected in thepreceding disclosure for illustration in specific terms for the purposeof describing these forms of the invention fully and amply for one ofaverage skill in the pertinent art, it should be understood that varioussubstitutions and modifications which bring about substantiallyequivalent or superior results and/or performance are deemed to bewithin the scope and spirit of the following claims. The entiredisclosures of U.S. patents and patent applications identified in thisapplication are hereby incorporated by reference herein.

What is claimed is:
 1. A film for use in transferring a thin layer ofmetal onto a substrate, the film having a thickness of about 4-75 μm andconsisting essentially of a polyester, and a release agent, in which thefilm comprises a core layer and a first skin layer coextensivelyadjacent in direct contact with one side of the core layer, a side ofthe first skin layer opposite the core layer defining a metal-contactingsurface, in which the release agent comprises surfactant selected fromthe group consisting of anionic surfactant, non-ionic surfactant and amixture thereof, and is uniformly distributed in the polyester of thefirst skin layer in amount effective to provide the metal-contactingsurface with a preselected adhesion value to a metal in the range ofabout 0.4-39 g/cm (1-100 g/in) measured by a 180 degree ethylene acrylicacid polymer peel test.
 2. The film of claim 1 in which the releaseagent of the first skin layer is effective to control the metal adhesionon the surface to within a range of ±3.9 g/cm (±10 g/in) of thepreselected adhesion value.
 3. The film of claim 1 wherein the film isbiaxially oriented and in which the polyester is polyethyleneterephthalate (PET).
 4. The film of claim 1 in which the film includesabout 0.1-1 wt % paraffin wax dispersed in the polyester.
 5. The film ofclaim 1 in which at least one of the core layer and the first skin layereach independently comprises a heterogeneous mixture of finely dividedsolid particles uniformly dispersed in a continuous phase of thepolyester, and in which the solid particles in the carrier film arepresent in concentration and size effective to provide themetal-contacting surface of the first skin layer with roughnesscharacterized by Ra at most about 50 nm and Sra at most about
 30. 6. Thefilm of claim 1 which further comprises a second skin layercoextensively adjacent in direct contact with the core layer oppositethe first skin layer, in which at least one of the core layer and thesecond skin layer each independently comprises a heterogeneous mixtureof finely divided solid particles uniformly dispersed in a continuousphase of the polyester, and in which the solid particles in the carrierfilm are present in concentration and size effective to provide themetal-contacting surface of the first skin layer with roughnesscharacterized by Ra at most about 50 nm and Sra at most about
 30. 7. Thefilm of claim 5 or 6 in which any solid particles in the core layer arepresent in the range of about 0.01 wt % to about 0.1 wt % and have sizeof about 0.5-1.0 μm.
 8. The film of claim 7 in which solid particles arepresent in the second skin layer in the range of about 0.01 wt % toabout 0.1 wt % and have size of about 0.1 μm to about 2.4 μm.
 9. Thefilm of claim 8 which exhibits a specular reflection of at least 160gloss units measured by glossmeter at a 60° angle.
 10. The film of claim9 further comprising a transferable layer of a metal in direct contactwith the metal-contacting surface of the first skin layer, the metalbeing selected from the group consisting of aluminum, copper, silver,titanium and a blend thereof, and the transferable layer having athickness equivalent to an optical density of about 0.2 to about 4, andin which the metallic layer on the metal-contacting surface the exhibitsa specular reflection of at least 830 gloss units measured by glossmeterat a 60° angle.
 11. The film of claim 1 further comprising atransferable layer of a metal in direct contact with themetal-contacting surface of the first skin layer, the metal beingselected from the group consisting of aluminum, copper, silver, titaniumand a blend thereof, and the transferable layer having a thicknessequivalent to an optical density of about 0.2 to about 4, and in whichthe metallic layer on the metal-contacting surface the exhibits aspecular reflection of at least 830 gloss units measured by glossmeterat a 60° angle.
 12. A method of transferring a metal to a substratecomprising the steps of: (A) providing a metal transfer film consistingof (i) a carrier film having a thickness of about 4-75 μm and consistingessentially of a polyester, and a release agent, in which the filmcomprises a core layer and a first skin layer coextensively adjacent indirect contact with one side of the core layer, a side of the first skinlayer opposite the core layer defining a metal-contacting surface, inwhich the release agent comprises surfactant selected from the groupconsisting of anionic surfactant, non-ionic surfactant and a mixturethereof, and is uniformly distributed in the polyester of the first skinlayer in amount effective to provide the metal-contacting surface with apreselected adhesion value to a metal in the range of about 0.4-39 g/cm(1-100 g/in) measured by a 180 degree ethylene acrylic acid polymer peeltest, and (ii) a transferable layer of the metal deposited in directcontact with the metal-contacting surface, the transferable layer havinga metal thickness equivalent to an optical density in the range of about0.2-4.0, (B) providing a substrate article having a surface coated withan adhesive layer, (C) contacting the transferable layer of the metaltransfer film with the adhesive layer of the substrate such that themetal transfer film bonds to the adhesive layer of the substrate, and(D) stripping the carrier film from the metal layer, therebytransferring the metal onto the substrate.
 13. The method of claim 12 inwhich the carrier film includes about 0.1-1 wt % paraffin wax dispersedin the polyester.
 14. The method of claim 12 in which the step ofproviding the metal transfer film further comprises obtaining a mixturecomprising a thermoplastic polyester resin and release agent, heatingthe mixture effectively to melt the thermoplastic polyester resin,uniformly dispersing the release agent in the thermoplastic polyesterresin, thereby forming a melt dispersion, forming a self-supporting filmfrom a polymeric composition comprising the melt dispersion, andstretching the film in a machine direction about 3×-6× and in thetransverse direction about 3×-6×, thereby causing the release agent tobloom to the outer surface of the carrier film.
 15. The method of claim12 in which at least one of the core layer and the first skin layer eachindependently comprises a heterogeneous mixture of finely divided solidparticles uniformly dispersed in a continuous phase of the polyester,and in which the solid particles in the carrier film are present inconcentration and size effective to provide the metal-contacting surfaceof the first skin layer with roughness characterized by Ra at most about50 nm and Sra at most about
 30. 16. The method of claim 12 in which thecarrier film further comprises a second skin layer coextensivelyadjacent in direct contact with the core layer opposite the first skinlayer, in which at least one of the core layer and the second skin layereach independently comprises a heterogeneous mixture of finely dividedsolid particles uniformly dispersed in a continuous phase of thepolyester, and in which the solid particles in the carrier film arepresent in concentration and size effective to provide themetal-contacting surface of the first skin layer with roughnesscharacterized by Ra at most about 50 nm and Sra at most about
 30. 17.The method of claim 16 in which any solid particles in the core layerare present in the range of about 0.01 wt % to about 0.1 wt % and havesize of about 0.5 μm to about 1.0 μm.
 18. The method of claim 17 inwhich solid particles are present in the second skin layer in the rangeof about 0.01 wt % to about 0.1 wt % and have size of about 1.0 μm toabout 2.4 μm.
 19. The method of claim 16 in which the carrier filmexhibits a specular reflection of at least 160 gloss units measured byglossmeter at a 60° angle.
 20. The method of claim 16 in which thetransferable layer of metal on the metal-contacting surface of the skinlayer of the carrier film exhibits a specular reflection of at least 830gloss units measured by glossmeter at a 60° angle.
 21. The method ofclaim 16 in which the metal on the substrate exhibits a specularreflection of at least 860 gloss units measured by glossmeter at a 60°angle.